Not Applicable
Not Applicable
1) Field of Invention
This invention relates to a manually propelled wheelchair. In particular, this invention encompasses the chair as a system using two levers that the user stokes, in a rowing motion, forward and backward with. Both the xe2x80x9cpushxe2x80x9d and xe2x80x9cpullxe2x80x9d stroke of these lever arms provide forward propulsion to the rear wheels. The two levers are mounted on each side of the chair while the remaining components (gears, shafts, bearings, clutches, internal shifting hubs, sprockets and chains) are located entirely under the seat of the chair. For reversing and indoor operation, the propulsion system can be disengaged. This allows the chair to be used in a conventional manner (by hand directly at the wheel handrails). An automatic shifting hub option is available that relies on sensory feedback from the rear wheels to intelligently determine which ratio of gears is best suited for terrain and speed.
2) Description of Prior Art
For persons having disabilities making walking impossible or difficult, chairs with wheels attached have traditionally been the standard means of transportation. These chairs typically have two small caster wheels on the front that can turn 360 degrees, and two larger wheels on the back for propulsion. The larger rear wheels have handrails attached to them that the user grasps and pushes forward repeatedly. This requires wrist and shoulder strength and often results in chronic stress injuries after extended use due to the poor ergonomics. In order to turn these wheelchairs, the operator grasps one wheel while pushing the other forward. Stopping is similarly done by grasping both rear wheels at the handrails. Thick leather gloves are often used in this grasp and release motion to aid in grip, and protect the user""s hands from injury. In addition, climbing hills can be nearly impossible, as the user must remove his or her hands from the rim on each subsequent stroke. This creates an inefficient system and loss of work as the force from gravity pulls backward on the chair.
The following prior patents are discussed hereinbelow:
U.S. Pat. No. 287,789, Arbogast;
U.S. Pat. No. 3,666,292 Bartos;
U.S. Pat. No. 3,994,509 Schaeffer;
U.S. Pat. No. 4,506,900 Korosue;
U.S. Pat. No. 4,560,181 Heron;
U.S. Pat. No. 4,811,964 Horn et al.;
U.S. Pat. No. 5,007,655 Hanna;
U.S. Pat. No. 5,263,729 Watwood;
U.S. Pat. No. 5,632,499 Hutcherson et al.;
U.S. Pat. No. 5,865,455 Taylor;
U.S. Pat. No. 6.158,757 Tidcomb; and
U.S. Pat. No. 6,234,504 Taylor.
Employing handles to aid in the propulsion of wheelchairs dates back to before the turn of the century. For example, U.S. Pat. No. 287,789 granted to Arbogast on Nov. 6, 1883, utilizes a wheelchair hand crank system in which the ground wheels of a wheelchair are driven by a chain which is also connected to the hand crank. The chain provides a smooth linkage between the hand crank and the ground wheel. However, to attain the leverage needed for easy operation, the hand crank must be extended to an awkward length.
U.S. Pat. No. 3,666,292 utilizes two lever arms that turn a crank mechanism attached to the rear wheels of the wheelchair. Steering is accomplished by individually turning the lever arms, which translates this motion to the front caster wheels with cables. This chair provides no means of gearing for various speed or terrain conditions. Also, since the steering is done with the front wheels, the turning radius is extremely large and not practical for indoor operation.
U.S. Pat. No. 3,994,509 includes two lever arm drive assemblies mounted on the outside of the chair. Each propulsion drive system utilizes one way clutches with idler sprockets to transmit unidirectional rotation to the ground wheel in both the push and pull stroke. This system uses a cable chain capable of reverse bending to wrap around the idler sprockets. The entire propulsion system adds to the overall width of the wheelchair. The complex reverse bending chain also makes maintenance and assembly very difficult. In addition, the need for a reversible-shifting hub, not currently available on the market, makes the design proposition extremely expensive to manufacture.
U.S. Pat. No. 4,506,900 focuses on utilizing a single lever arm to propel the wheelchair with one hand (either the right or left side is possible). It provides a forward, reverse and neutral lever position to aid in maneuverability. It, however, offers no means of gearing, and can only be turned by placing the lever in a neutral position and manipulating the wheelchair by hand at the wheels.
U.S. Pat. No. 4,560,181 contains two lever arms that drive a ratchet wheel located on the rear wheel axle in both the forward and reverse stroke. The forward stroke engages one ratchet while the other is disengaged and reverses this action for the return stroke. By changing where the ratchet wheel is connected to the lever arm, a continuously variable gear ratio is possible. However, this adjustment can not be made while the chair is in motion, and it also will either increase or decrease the length of possible stroke available to the lever arm.
U.S. Pat. No. 4,811,964 uses a single lever arm located between the operator""s legs. This drives two separate sprockets on one rear axle which employ ratcheting mechanisms with chains attached to cables. The cable is run through an idler pulley such that both the push and pull stroke transmits power to the rear wheels with no loss of work. Due to the single rear axle, conventional wheelchair turning (braking one wheel while powering the other) cannot be used. Instead, the lever arm acts as the turning mechanism through a pivoting universal joint. This increases the overall turning radius of the chair making it impractical for tight corners or indoor use. There are also no provisions for gearing or gaining mechanical advantage through other means to adjust the speed.
U.S. Pat. No. 5,007,655 uses a pair of lever arms on each side of the chair, each of which is connected to a sprocket on the rear drive wheels through a rack-and-pinion engagement. A one-way clutch is used to effectively drive the sprocket during the power stroke. After the power stroke is complete, the lever arm is retracted as the one-way clutch disengages from the rear drive wheel. This produces a wasted return stroke and loss of work for the user. The wheelchair has provisions for changing the leverage applied to the sprocket by moving where the lever arm attaches to the rack-and-pinion engagement. It does not, however, provide a means of easily changing this lever advantage while pumping the lever arms.
U.S. Pat. No. 5,263,729 uses a structure mounted to an existing wheelchair frame. A lever extends from the inside of the rear wheel axles up to the user. It contains a prawl that has teeth on it and extends over the tire of the wheel. These teeth provide positive contact with the tire during the pushing stroke and release during the return stroke. This invention has the disadvantage of a lost return stroke with no work generated, and also no means of gearing or gaining mechanical advantage are provided.
U.S. Pat. No. 5,632,499 is a wheelchair system using a pair of lever arms that drive self contained planetary gears. These gears are designed such that both the forward and reverse stroke drive the rear wheel in the forward direction. There are, however, no provisions made for dynamically gearing the system, and the complexities of the small, planetary gears make service and maintenance difficult.
U.S. Pat. No. 5,865,455 is a wheelchair using two push levers as its propulsion system. This chair employs standard bicycle sprocket clusters mounted on the rear axles with chains connecting to the front push lever drive system. A standard bicycle derailer is mounted on each axle to change gear ratios and thus speeds. This system uses a ratchet mechanism in the push levers to change between forward, neutral and reverse directions. It does not provide a means of using both the push and pull stroke to transmit unidirectional motion to the rear wheels. Therefore, one stroke, either the push or pull is a wasted return stroke and loss of work.
U.S. Pat. No. 6,158,757 uses a flexible motion conversion, such as a cable, to transmit the lever""s pushing power directly to a drum attached to the rear wheel. This reduces complexity in gearing, chains and sprockets, but only transmits power during the pushing stroke. Again, the disadvantage to this system is a wasted return stroke with loss of work. Also, the only provisions made for changing mechanical advantage is by lengthening or shortening the lever arm. No changeable gears or hubs are used to adapt the chair to various speeds or terrain.
U.S. Pat. No. 6,234,504 B1 is a continuation of U.S. Pat. No. 5,865,455 described above. It employs the same principal, but has further descriptions and drawings of the invention.
We have invented a manual wheelchair that comprises a propulsion system located entirely under the seat of the chair. Two lever arms, positioned on the side of the chair, actuate the propulsion system and provide forward motion with both the push and pull stroke. This is accomplished using drive and idler gears fitted with one-way clutches or ratcheting mechanisms that transmit the power to the rear wheel through sprockets and chains.
The drive gears are linked to an internal shifting hub that is either manual or automatic in nature. The manual shifting option uses conventional bicycle shifting levers to change gears during operation. The automatic shifting hub option contains sensory feedback from the rear wheel, a shifting motor, and a central processing unit to automatically determine the most efficient gear available for terrain and speed.
A disconnecting clutch is located on the rear axle to disengage the entire propulsion system from the chair. This enables the user to reverse the chair, and also use it as a conventional wheelchair in very tight quarters (such as indoor operation). The disconnecting clutch employs two springs, one in compression and one in tension, to aid the user in disengaging the propulsion system under load.
Using quick release draw clamps, the entire chair is easily separated into three pieces comprising of; the seat, the right half propulsion system and the left half propulsion system. This makes transportation in vehicles practical. Also, the seat of the wheelchair can be moved forward or backward to accommodate getting into and out of the chair, as well as moving the effective center of gravity for stability and traction control.